Contact lenses have been used commercially to improve vision since the 1950s. The first contact lenses were made of hard materials. Although these lenses are still currently used, they are not suitable for all patients due to their poor initial comfort and their relatively low permeability to oxygen. Later developments in the field gave rise to soft contact lenses, based upon hydrogels, which are extremely popular today. Many users find soft lenses are more comfortable, and increased comfort levels can allow soft contact lens users to wear their lenses longer than users of hard contact lenses.
A hydrogel is a hydrated crosslinked polymeric system that contains water in an equilibrium state. Hydrogels typically are oxygen permeable and biocompatible, making them preferred materials for producing biomedical devices and in particular contact or intraocular lenses.
Conventional hydrogels are prepared from monomeric mixtures predominantly containing hydrophilic monomers, such as 2-hydroxyethyl methacrylate (“HEMA”) or N-vinyl pyrrolidone (“NVP”). U.S. Pat. Nos. 3,220,960, 4,495,313, 4,889,664, and 5,039,459 disclose the formation of conventional hydrogels. Blends of such mixtures are cured, typically, using heat or light activated initiators. The time required to cure such blends typically ranges from a few minutes to more than 24 hours. In commercial processes, it is preferable that the cure times be short. The resulting polymers are swelled in water. The absorbed water softens the resulting hydrogels and allows for some degree of oxygen permeability.
The present invention relates to the discovery of a silicone polymer/silicone hydrogels containing 2-hydroxyethyl acrylamide and ophthalmic devices, such as contact lenses, formed therefrom, which have improved curing speed and other properties.